Biology Reference
In-Depth Information
and amphibians probably stems from the interaction of two factors. First, most of
these species are cryptic and insectivorous, making their true densities difficult to
perceive and obviating any direct impact on humans or their economically
important domesticated animals. Hence, alien reptile and amphibian populations
are easy for most people - including most scientists interested in invasive species
- to overlook or ignore. Second, much of the literature on these introductions is
widely scattered in obscure sources and has previously been unsynthesized (but
see Lever, 2003, for a partial, though fairly comprehensive, summary), making it
difficult to develop an overall appreciation for the magnitude of reshuffling that
has occurred or how it has developed.
This situation has begun to change over the past 25 years. The rapid spread of
cane toads across Queensland by the 1970s, combined with anecdotal reports of
their poisoning of native wildlife (Breeden, 1963; Rayward, 1974; Covacevich and
Archer, 1975), led to considerable government funding to elucidate these effects,
understand the biology of the toad, and identify means by which to control it (Tyler,
2006; T. Robinson et al., 2006). The results of this work were a fairly broad under-
standing of toad expansion, genetics, and parasites within Australia (cf. Appendix A).
However, these efforts failed to identify practical control mechanisms, and the
toad continues to expand its range rapidly. More effective in bringing attention to
herpetological introductions was recognition that the brown treesnake (
Boiga
irregularis
) was responsible for the spectacular decimation of Guam's native forest
bird fauna (Savidge, 1987a; Savidge et al., 1992), which largely disappeared by the
mid-1980s. Lost from Guam were ten species of forest birds, three seabirds, two
bats, and six lizards within approximately 40 years (Savidge, 1987a; McCoid,
1991; Rodda and Fritts, 1992; Fritts and Rodda, 1995, 1998; Rodda et al., 1997,
1999a). Three of the birds and one bat were endemic to Guam and are now globally
extinct. Two more birds - a rail and a kingfisher - remain only in captivity for the
time being. Most of the few native vertebrates that remain on Guam do so at
extremely reduced numbers. This was an unanticipated effect from a “mere snake”
(J.T. Marshall, 1985), and most ornithologists at the time blamed pesticides or
disease for the bird declines (Jaffe, 1994). Consequently, Savidge's evidence and
arguments laying responsibility (dare I say) at the feet of the snake were initially
dismissed as impossible. The effect of these losses has been a wholesale change in
food webs on Guam, with broader ecosystem effects - such as loss of pollinators
and changes in vegetation communities - anticipated (Fritts and Rodda, 1998), sup-
ported by some data (Perry and Morton, 1999; Ritter and Naugle, 1999), but not yet
rigorously tested. Similarly, beginning in the late 1980s, evidence began to accu-
mulate indicating that the bullfrog (
Rana catesbeiana
) is at least partly responsible
for the decline of a diversity of native frogs and snakes across the western United
States (see Chapter 3). It has also recently been shown to be a likely vector in the
spread of chytrid fungus, which has decimated native frog populations around the
globe in the past 20 years (Hanselmann et al., 2004; Garner et al., 2006).
The approximately simultaneous acquisition of evidence linking brown tree-
snakes, cane toads, and bullfrogs to damage to native species has helped foster a
growing awareness of the potential ecological importance of invasive reptiles and
